The invention relates to a cap device used for various types of fuel tanks installed in, for example, an automobile for opening and closing an opening portion of the tank.
FIGS. 20(a) and 20(b) show a conventional cap device disclosed in Japanese Patent Publication (TOKKAI) No. 2001-348050. As shown in FIG. 20(a), a cap device 80 includes a main portion 81 having a cover 84 rotatably attached to an upper flange 83 of a shaft portion 82, and a torque mechanism 85 disposed between the upper flange 83 and the cover 84. The main portion 81 also includes a sealing member 86 mounted on an upper side of the shaft portion 82 and a projection 87 disposed on a lower side of the shaft portion 82 as an engaging portion.
As shown in FIG. 20(b), when the main portion 81 is inserted into an opening portion 91 of a tank 90 along an insertion notch 92, and is rotated by a predetermined angle (90°) in a closing direction from the inserted state, the sealing member 86 is pressed against an edge 91a of the opening portion 91 while deforming, and the projection 87 engages the engaging portion (a lower surface of a step) 93 inside the opening portion (a cap mounted state). Also, the projection 87 is formed of the first inclined surface 87a having a large angle and the second inclined surface 87b having a medium angle relative to the engaging portion 93, so that a rotational torque is changed from an initial stage to a later stage when it is rotated by the predetermined angle in the closing direction. The torque mechanism 85 includes an engaging portion (not shown) provided on the cover 84, a torque plate 88, and a spring. A reference symbol V represents a valve mechanism for controlling a pressure in the tank.
In the above structure of the conventional device, when the main portion 81 is rotated by the predetermined angle, at the beginning, the first inclined surface 87a is designed to have the large angle to prevent the rotational torque from becoming a large load due to the deformation of the sealing member 86, and in the final stage, the second inclined surface 87b is designed to have the medium angle to ensure the sealing. Further, instead of a latching structure where a cover rotates without resistance with respect to the main portion, the torque mechanism 85 is provided to create a resistance when the cover 84 receives a rotational torque larger than a predetermined torque, thereby securing the cap mounted state. Also, the cover 84 can be returned to the initial position with respect to the main portion 81 due to an urging force and a releasing operation of the spring of the torque mechanism.
Incidentally, for the fuel tank installed in the automobile, since the cap device 80 is frequently opened or closed, it is important that the cap device 80 is easy to detach and has a long life without abrasion and deterioration. Also, when the cap device 80 receives an improvident force due to a collision, accident or the like, it is important to prevent the fuel from leaking due to the force in the opening direction as well as damage due to the force in the closing direction. In the cap device 80 as described above, the abrasion and deterioration less likely occur as compared with a screw type, and it is easy to detach. However, it is preferable that the cap device can be operated with a lower force while maintaining the sealing for women and senior people, since the self-fueling system becomes more popular. Also, the conventional cap device does not meet sufficient reliability when the improvident force in the opening direction as described above is applied.
In view of the above problems, the present invention has been made, and an object of the invention is to provide a cap device for the fuel tank, wherein the cap device can be detached with a greatly reduced force in one-touch operation, even when the engaging portion of the cap engages the opening portion with a large force.
Another object of the invention is to provide a cap device for the fuel tank, wherein even when the improvident force is applied, the engaging portion of the cap is not disengaged from the engaging portion of the opening portion, thereby securely preventing the fuel leakage and improving the reliability.
Further objects and advantages of the invention will be apparent from the following description of the invention.